Control system for a pump



June l5, 1965 n. B. PURYEAR CONTROL SYSTEM FOR A PUM? 2 sheets-snee; 1

Filed Aug. 13, 1962 HI .MHH

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ON mm Mm. w NN United States Patent O 3,188,971 CONTROL SYSTEM FDR A PUMP David Il. Puryear, St. Joseph, Mich., assigner to The Bendix Corporation, St. Joseph, Mich., a corporation of Delaware Filed Aug. 13, 1962, Ser. No. 216,593 Claims. (Cl. 10S- 162) This invention relates to a pump, and more particularly to a control system for a variable displacement pump.

Automatic controls for variable displacement pumping structures are in wide use. The most commonly utilized systems of automatic control are those in which the pumping mechanism is either flow compensated or pressure compensated. A flow compensated lsystem is one in which the displacement of the pumping mechanism is automatically reduced as the fluid output tends to exceed a predetermined maximum or automatically increased as the fluid output tends to fall below a predetermined minimum. A pressure compensated system is one in which the displacement of the pumping structure is reduced as the pressure in the outlet line of the device tends to exceed a predetermined maximum.

It is an object of the invention to provide a variable displacement pump with a flow control for maintaining constant pump output.

' It is another object of the invention to provide a variable displacement pump with a control system which not only has a flow control for maintaining constant pump output but also a pressure control for controlling the maximum pressure in the pump outlet. A further object of the invention is to provide a variable displacement pump with the combination of a flow control and pressure maintaining control wherein the response of one control does not affect the response of the other control.

An over-all object of the invention is to achieve the above objects with structure which is simple and economical to produce.

Further objects and advantages of the present invention will become apparent from the following description, reference being made to the accompanying drawings wherein a preferred form of the present invention is shown; In the drawings:

FIGURE l is a section view illustrating a flow control valve and a pressure control valve in neutral positions;

FIGURE 2 is a view illustrating the flow control valve in one of its operating positions while the pressure control valve is in neutral position;

FIGURE 3 is a view illustrating the flow control valve in a 'different operating position while the pressure control valve is in neutral position; and

FIGURE 4 is an illustration of the flow control valve and the pressure control valve in operating positions.

Referring to FIGURE 1, there is shown a pump rotor mounted for rotational movement relative to a port plate 12. Pistons 14 are displaceable Within the rotor and the stroke of the pistons are controlled by the angle of the swash plate 16, which angle is controlled by slidable movement of a servo piston 18 within a cylinder bore 20. A pair of trunnion balls 24 (one of which is shown) defines an axis about which the swash plate rotates. Rotation of the swash plate is effected by movement of the piston 18 which movement is transferred to the swash plate through a thrust link 22. The interior of the rotor 10 and the association of the pistons 14 and port plate 12 therewith may be of any well known construction as for instance the structure illustrated in applicants copending application U.S. Serial No. 778,538 filed December 5, 1958 (common assignee), now U.S. Patent No. 3,070,031. An outlet passage 26 is connecte-:i to an outlet port of 3,188,971 Fatenteel .lime l5, 1965 the port plate 12 and has a restriction 28 therein. The passage 26 upstream of the restriction 28 is communicated to the one end 30 of a slidable flow control valve spool 32 and to one end 34 of a slidable pressure control valve spool 36 by passages 38 and 40 respectively. The passage 26 downstream of the restriction 28 is connected to the other end 45 of the flow control Valve spool 32 and the chamber 33 by a passage 39. The interior 42 of the pump body is communicated by a passage 44 to a drain and is maintained at low pressure. The low pressure in the interior 42 is communicated to the other end 46 of the pressure control valve spool 36 and to a chamber 48 by a passage 50 and a passage 52 communicates the low pressure in chamber 48 to the bore 29. A passage 54 interd connects the tlow control valve spool and pressure control valve spool bores 29 and 35 and the passage 56 interconnects the pressure control valve spool bore 35 with the servo piston cylinder bore 20.

The volume of flow across the restriction 28 may be determined as follows: f

Let:

Q=the volume of fluid passing through said restriction `at a given rate of time /l--the area of the orifice 28 C=the coefficient of discharge of the restriction g: gravity force AP=the pressure drop across the restriction 28 since A, C, and 2g remain constant, AC\/2g may be replaced by K which equals a constant. It then follows that:

In other words the quantity or flow varies as the square root of the pressure drop across the restriction or is a function of the pressure drop across the orice 28. Therefore, for a given rate of flow there will be a given pressure drop across the orifice.

Since the pressure downstream of restriction 28 in passage 26 is communicated to the end 45 of the flow control valve spool 32 by passage 39 and the pressure upstream of restriction 2S in pass-age 26 is communicated to the end 36 of the flow control valve spool 32 by passage 38, the pressure drop across restriction 28 may be sensed by the valve 32 thereby controlling the output ow Of the pump in a manner to be described hereinafter.

The slidable ilow control valve spool 32 has a pair of spaced lands 58 and 60 and another land 62 spaced from the land 58. As can be seen, communication between the passages 52 and 38 are always cut off from each other by the lands 58 and 60 no matter in which direction the valve spool 32 is moved, In the neutral position illustrated in FIGURE l, the land 58 separates passage 52 from passage 54 and the land 60 separates the passage 38 from passage 54. With reference to FIGURE 2, when the valve member 32 is in an operating position shown therein the land 58 communicates passage 52 with passage 54 and when the valve member 32 is in an operating position as shown in FIGURE 3 the passage 38 is communicated with passage 54.

The pressure control valve spool 36 has a pair of spaced lands 64 and 66. In the normal position of valve spool 36 illustrated in FIGURE l, it can be readily seen that the land 64 communicates the passage 54 with passage 56 and separates passages 54 and 56 from the passage 40; passage 40 being always separated from passage 54. When the valve spool 36 is in an override position as shown in FIGURE 3 passage 54 is separated from passages 56 and f Y i s f ,f Y 40 by the land 64 and passage ft-ris'communicated with passage 56 by the land 66.

Springs 68 are Vcompressed between a seat 70 of their respective valve spools and a retainer cup 72 for biasing their respective valve spools against the upstream pressure acting on the ends 30 and 34 of their respective valve spools. The compression of the springs 68 are adservo pist-on 18 upwardly and lowering the' swash plate angle and the output of the pump.

.Referring to FIGURE 4 and assuming that iiow has dropped and therefore the pressure drop across the restricjustable by turningl an kadjusting screw 74 and renders possible the operation of the valve members 32 and 36 for different values of constant flow desired and maximum pressure desired. Y

" 'Operation Referring to FIGURE l, assuming thaty the pressure Y vdrop across the restriction 28 corresponds to that set by the flow contr-ol valve member 32 for the normal position and the pressure upstream Vin passage 26 isbelow the maximum set for the pressure control valve 36, then the servo piston 18 remains in'its set position sincerthe pressure ac't-` ing thereon is contained within passages 56 and `54 and maximum allowed by the pressure 'controlV valve spool 36, then :the combinedfforces resulting from the'downstream pressure and the spring' acting Von the end 45 ofthe flow control valvespool 32 will'be greater than the forceresulting from the -upstream pressure acting onr the end 30 of the ilow control valve member 32 thereby resulting in the valve member 32 being biased downwardly vand communicating passage 52 to passages 54 andy 56 to Y the servo piston 18; the passage 54 being communicatedV to passage 56 since the valve member 36 is still in normal Y position. The pressure in chamber`v 20 will bleedk via the Y passage 52, chamber 48 and passage 50 to the drain resulting in the piston 18 being lowered and the swash plate angle being raised to increase the stroke of the pistons and therefore the output of the pump` l Y Now referring to FIGURE 3 and assuming that the pressure drop across the restriction 28' is greater than that allowed by the ilow control valve spool 32 (therefore ow has increased) and the upstream pressure in 'passage 26k is less than the maximum allowed by the pressure control valve spool 36, then the upstream pressurey inpassage 38 acting upon the end 30 of slidable flow control valve spool 32 will produce' a force.Y greater 'than the force of the downstream pressure and spring 68 actingron Vthe ,50

other end 45 of the ow control valvespool 32 to bias the valve` spool 32 upwardly to communicate the passage v38 tion' is less than that allowed by the ow control valve member 32 and the upstream pressure in passage 26 is greater thanthat allowed by thepressure control valve spool 36, ,then the flow control valve 32 willtbe biased downwardly communicating the low pressure passage 52 VVwith ipassage 54. However, the pressure control valve 36 will override the flow control valve since the upstream pressure in passage 40 actingV on the endV 34 of the pressure control valveA spool 36;` will produce a greater force than the combined force produced by the low pressure in f chamber 48 and the spring 68 acting on the end 46 of the valve vspool 36 thereby moving the pressure control valve spool 36 and cutting offcommunication between passages 5'4- and 56 by the land 64 and communicating the passage 40 and therefore the `upstream pressure with the passage 56 and the servo piston i8 by land 66. The piston 1E 'will bey raised thereby reducing the swash plate angle and ther stroke of the pistonsancl Vthe'output of the pump asV called.. for by the pressure control valve instead oi increasing the angle of the swash plate and raising the output` of the pump as calledffor bythe flow control valve.' When the flow control yalve 32 is attempting tc communicate the chamber 20 with the low pressure pas' 'Y sage 52 `andthe pressure control valve 36 is trying tc "communicatethe upstream pressure passage `with'the passage 56 andthe chamber r2tlg-there may be a slight period `wherein passages 54 and 56 are comrnunicatec with each'ctherbefore the land 64 cuts olf such com munication. However, ifk such communication is effected the lag before land 64 cuts off such communication i: not considered tothe critical.`

Thus, it can be seen that applicant has achieved a con y trol system wherein 'the system may control yflow pro duced by the pump regardless of an increase in speed o rotation of the rotor :or a decrease in speed of rotatiol of the rotor and also hask a pressure control which op erates independentlyrof theflow control and override the 4flow control whenV pressure in the system exceed a predetermined amount. Of course, the ilow contro will operate to maintain a constant ow only during th| period when certain'conditions reside in the pump. Thi

' pump rotor must be .rotating at Vwithin a certain mini with the passage 54. Upstream pressure will be com- ,i

municated to the passage 56 Yand to the Vservo piston 18 biasing the piston upwardly to lower the swash plate anv rgle and the output of the pump since the pressure Vcontrol valve spool 36 is still'in normal position. Y

Assuming there is a set amount of flow and therefore the pressure drop across the restriction 28 is as'allowed by the flow control valve spool 32 and the upstream pressure in passage 26 is greater thanthat allowed by the pressure control valve spool 3,6, then the pressure control mum orY maximum speed and the pressure must be Withii 'a' certain minimum', or lmaximum value in addition t1 some1 other minor variable before the pump will bi capable Aof giving'a certain ilow required.

While the form ofthe embodiment ofthe inventioi as herein disclosed constitutes a preferred form, it i to, be understood that other forms may be adopted, al coming withinrthe `scope of the claims which follow. rIclairn: f

1. The combinationrof a variable displacement pumj and a control system therefor, comprising: Vfluid opel rated control means for varying the output of said pum; said `pump having an outlet port; rst passage mean communicatingwith said outlet port; a flowrestrictio ini-,said `rfirst. passage means separating said first passag valve spool36 will be biased upwardly thereby communi- Y 'Y eating the passage 40 with the pass-age 56 for moving the piston 18 upwardly and lowering the swash plate Vangle and the output of the pump.y Y Y, f r

Assuming thatr flow has increased and therefore there is too great a pressure drop across the restriction 28 and that the upstream pressure in passage '26 is greater than that allowed by the pressure control'valve 36V, then both control valves will bev biased .upwardly with each control valve vtending to helpV each other since the result oftheir means intotwo portions; `first valve means' commun: cated with both'portions of said first passage mean: secondV passage means communicating lsaid rst valv means with said fluid operated control means; secon valve meansI located in said second passage means an communicated with said `first rpassage means; third pa: sage means communicating a'low pressure source t said iirstvalve means; said first valve means being so ai rangedand constructed that it communicates with sai third passage means with said `second passage means i v one operating position, communicates said first passag movements would be to communicate the upstream pressure in passages 38 and 40 with the passages S4 and 56 respectively which lead to the chamber20 for biasing the means ywith said second passage means in a second ope: ating position, and cutsoff rsaid ksecond passage mear from; said first passage means and said third passag means in a third operating positron; said second valve means being so arranged and constructed that it communicates said first valve means with said fluid operated control means in a normal position and cuts olf communication between said first valve means and said fiuid operated control means while communicating said first passage means to said fluid operated control means in an override position, said first valve means being responsive to the pressure differential across said flow restriction; said second valve means being responsive to pressure beyond a predetermined limit in one of said portions of said first passage means; whereby said fluid operated control means will be controlled by said first valve means when the pressure in said one portion of said first passage means is below said predetermined limit and said fiuid actuated control means will be controlled vby said second valve means when the pressure in said one portion of saidfirst passage means is beyond said predetermined limit.

2. The combination of a variable displacement pump and a control system therefor, comprising: fiuid operated control means `for varying the output of said pump; said pump having an outlet port; first passage means communicating with said outlet port; a flow restriction in said first passage means; first valve means communicated with said rst passage means upstream and downstream of said flow restriction; second passage means communicating said first valve means with said fluid operated control means; second valve means located in said second passage means and communicated with said first passage means upstream of said flow restriction; third passage means communicating a low pressure source to said first valve means; said first Valve means being so arranged and constructed that it communicates said third passage means with said second passage means in one operating position, communicates said first passage means upstream of said flow restriction with said second passage means in a second operating position, and cuts off said second passage means from said first passage means and said third passage means in a third operating position; said second valve means being so arranged and constructed that it communicates said first valve means with said fluid operated control means in a normal position and cuts off communication between said first valve means and said fluid operated control means while communicating said first passage means upstream of said fiow restriction to said fluid operated control means in an override position; said first Valve means being responsive to the pressure differential across said [iow restriction; said second valve means being responsive to pressure beyond a predetermined limit upstream of said flow restriction to move from said normal to said override position; whereby said fluid operated control means will be controlled by said first Valve means when the pressure upstream of said restriction is below said predetermined limit and said fiuid operated control means will be controlled by said second valve means when the pressure in said first passage means upstream af said restriction is beyond said predetermined limit.

3. The combination of a variable displacement pump 1nd a control system therefor, comprising: fiuid operated control means for varying the output of said pump; ;aid pump having an outlet port; a first passage means :ommunicating with said outlet port; a flow restriction n said first passage means; first Valve means communi- :ated with said first passage means upstream and downatream of said flow restriction; second valve means :ommunicated with said first passage means upstream )f said fiow restriction; -second passage means inter- :onnecting said first and second valve means, third pasage means communicating said second valve means with aid fluid operated control means; fourth passage means :ommunicating a low pressure source to said first valve neans; said first valve means being so arranged and :onstructed that it communicates with said fourth passaid second passage means from said first passage means.

and said fourth passage means in a third operating position; said second Valve means being so arranged and constructed that it communicates said second passage means with said third passage means in a normal position and cuts of communication between said second passage means and said third passage means while com-l municating said first passage means upstream of said flow restriction to said third passage means in an override position; said first valve means being responsive to the pressure differential across said flow restriction; said second valve means being responsive to pressure beyond a predetermined limit upstream of said flow restriction to move from said normal to said override position; whereby said fluid operated control means will be controlled by said first valve means when the pressure upstream of said restriction is below said predetermined limit and said fluid operated control means will be controlled by said second valve means when the pressure in said first passage means upstream of said restriction is beyond said predetermined limit.

4. The combination of a variable displacement pump and a control system therefor comprising: fluid operated control meansl for varying the output of said pump, said pump having an outlet port, a first passage means communicated with said outlet port, a ow restriction in said first passage means, a first bore having a first movable valve member therein, second passage means communicating pressure downstream of said restriction to one end of said first movable valve member for biasing the Valve member in one direction, third passage means communicating pressure upstream of said restriction to the other end of said valve member biasing said first valve member in the opposite direction, a second bore having a second movable valve member thereon, fourth passage means communicating said first bore with said second bore, fifth passage means for communicating said first bore with low pressure, said first valve member closing off said fourth passage means from said fifth and third passage means when in neutral position and said fifth and third passage means from each other at all times, said first movable valve member communicating said fourth and third passage means when moved in said opposite direction and communicating said fourth and fifth passage means when moved in said one direction, sixth passage means communicating said second bore to said fiuid operated control means, seventh passage means communicating said upstream pressure with one end of said second valve member urging the same in an override position, means for biasing said second valve member into a normal position, said second Valve member when in said override position communicating said sixth and seventh passage means and cutting off communication between said fourth passage means and said sixth passage means and when in said normal position cutting olf said sixth and seventh passage means communication and communicating said fourth passage means with said sixth passage means, whereby said fluid operated control means will be controlled by said first valve member when the pressure upstream of said restriction is below the limit determined by said biasing means and said fluid operated control means will be controlled by said second valve member when the pressure in said first passage means upstream of said restriction is beyond the limit determined by said biasing means.

5. The combination of a variable displacement pump and a control system therefor comprising: fluid operated control means for varying the output of said pump, said pump having an outlet port, a first passage means communicated with said outlet port, a flow restriction in said first passage means', a first bore having a first spool sliddirection,4 third. passage: means .communicating pressure Upstream of said restriction Vtqthe other end of said rst spool member biasing saidrstspool in theY opposite direction; Yfourth passage means 'communicatingV said rst bore with low pressure, a secondbore anda second spool slidable therein, ifth passage means communicat- Y ing said rst bore with said secondv bore, said r'st spool having a pair of annular lands at saidother end and a land spaced fromfone ,of said pair of landsdeining .an yannular grooveA therebetween, said annular groove bridging said fourth passage means and v,saidfipair' of lands bridging said fth passage means'whensaid spool isrin neutral rposition,`they other of said pair of lands communicating saidthrd and fifth passage meanswhen Y said'spool is moved in said opposite-direction and said groove communicating said fourth and fth pasrsageimeansVV when said spool is moved in 'saidYone'direction,l sixth passage meanscommunicating saidjpsecond bore with said fluid control mea'nsfseverith'V passage means communieating said upstream'filuid,y pressure with one end of said second spool and'biasing saidrspool into an override-position, means for biasing said secondvspool into a norv rnular groove therebetween which bridges said fth an( sixth passagel means when inmormal position and wher biased substantially into override position, saidV one o: said spaced lands; will' cut oi .communication of sai( fth Vandsixth passagemeans andthe other ofsaid spacer lands kwill communicate ,said sixth and' seventh passags means, whereby said uid, operated control means wil be controlled by `said rstj spool member when the pres sure upstream4 of said-restriction,fisbelowthe limit de 10 termined by.said biasing means .and said' fluid operate j control rneansfwll bercontrolled `by said jsecond spoo member whenv the pressure, in .said irstf passage mean upstream 'of saidA restriction isbeyondr the limit deter Y mined by said biasing means.'- 15 I Y, 'i

References Cited by theExamincr n -`UYNITED STATES PATENTS Y2',2?:8,061 4/41 Kendrick.V ,103---12` 20 2,600,632 6752Y French r v r 103-12 2,845,876 8/58 Keel 103-4 2,888,810 6/59k Hann g 103--16 `2,896,546,V 7/59 vLundgren et alll 1 '7 103-12 '42,975,717 3/611 'Rynders etal. c 103-12 25 ,Y 3,002,462 A10/6'1 Raymond T 1033 A3,064,583 l1/62 kBurt ,103--12 3,067,693 12/ 62 mal position, saidA second spool havingy ajpairnof annular lands at said one end thereofY anda land spaced from one of said last named pairjof` lands defining an anv Lambeck j j s -103-3 LAURENCE .,V. EFNER', Primary Examiner. 

1. THE COMBINATION OF A VARIABLE DISPLACEMENT PUMP AND A CONTROL SYSTEM THEREFOR, A COMPRISING: FLUID OPERATED CONTROL MEANS FOR VARYING THE OUTPUT OF SAID PUMP; SAID PUMP HAVING SAID OUTLET PORT; FIRST PASSAGE MEANS COMMUNICATING WITH SAID OUTLET PORT; A FLOW RESTRICTION IN SAID FIRST PASSAGE MEANS SEPARATING SAID FIRST PASSAGE MEANS INTO TWO PORTIONS; FIRST VALVE MEANS COMMUNICATED WITH BOTH PORTIONS OF SAID FIRST PASSAGE MEANS; SECOND PASSAGE MEANS COMMUNICATING SAID FIRST VALVE MEANS WITH SAID FLUID OPERATED CONTROL MEANS; SECOND VALVE MEANS LOCATED IN SAID SECOND PASSAGE MEANS AND COMMUNICATED WITH SAID FIRST PASSAGE MEANS; THIRD PASSAGE MEANS COMMUNICATING A LOW PRESSURE SOURCE TO SAID FIRST VALVE MEANS; SAID FIRST VALVE MEANS BEING SO ARRANGED AND CONSTRUCTED THAT IT COMMUNICATES WITH SAID THIRD PASSAGE MEANS WITH SAID SECOND PASSAGE MEANS IN ONE OPERATING POSITION, COMMUNICATES SAID FIRST PASSAGE MEANS WITH SAID SECOND PASSAGE MEANS IN A SECOND OPERATING POSITION, AND CUTS OFF SAID SECOND PASSAGE MEANS FROM SAID FIRST PASSAGE MEANS AND SAID THIRD PASSAGE MEANS IN A THIRD OPERATING POSITION; SAID SECOND VALVE MEANS BEING SO ARRANGED AND CONSTRUCTED THAT IT COMMUNICATES SAID FIRST VALVE MEANS WITH SAID FLUID OPERATED CONTROL MEANS IN A NORMAL POSITION AND CUTS OFF COMMUNICATION BETWEEN SAID FIRST VALVE MEANS AND SAID FLUID OPERATED CONTROL MEANS WHILE COMMUNICATING SAID FIRST PASSAGE MEANS TO SAID FLUID OPERATED CONTROL MEANS IN AN OVERRIDE POSITION, SAID FIRST VALVE MEANS BEING RESPONSIVE TO THE PRESSURE DIFFERENTIAL ACROSS SAID FLOW RESTRICTION; SAID SECOND VALVE MEANS BEING RESPONSIVE TO PRESSURE BEYOND A PREDETERMINED LIMIT IN ONE OF SAID PORTIONS OF SAID FIRST PASSAGE MEANS; WHEREBY SAID FLUID OPERATED CONTROL MEANS WILL BE CONTROLLED BY SAID FIRST VALVE MEANS WHEN THE PRESSURE IN SAID ONE PORTION OF SAID FIRST PASSAGE MEANS IS BELOW SAID PREDETERMINED LIMIT AND SAID FLUID ACTUATED CONTROL MEANS WILL BE CONTROLLED BY SAID SECOND VALVE MEANS WHEN THE PRESSURE IN SAID ONE PORTION OF SAID FIRST PASSAGE MEANS IS BEYOND SAID PREDETERMINED LIMIT. 